1. Field of the Invention
The present invention is directed to an X-ray diagnostic device for mammography examinations having an arm for an X-ray tube and a subject table as well as a compression plate arranged between the X-ray tube and the subject table, the compression plate being connected to the arm and being displaceable along it, wherein the arm can be rotated around a horizontal shaft and is height-adjustable along an imaginary longitudinal axis of a stand.
2. Description of the Prior Art
An X-ray diagnostic device of this type is disclosed in European Application Patent 0 370 089. In this device, the rotational axis of the arm lies outside the center of gravity of the arm. In order for the arm with the X-ray tube, the compression plate and the subject table to be able to be rotated around the rotational axis, the free end of the rotational axis is provided with a gearwheel rigidly connected to this end that is driven by a comparatively strong and thus comparatively large, motor. A pneumatic spring device serves for additional weight compensation of the arm. The vertical displacement of the arm ensues with a motor and a toothed rack that are arranged separately from the rotational device of the arm.
In a routine examination of a breast of a patient, a first vertical exposure and subsequently a second exposure are made, with the arm being rotated by an angle between 45° and 60° between the two exposures. An exposure when the arm has been turned by approximately 90° also can be made in conjunction with a further examination. In order to avoid the patient having to step aside given rotation of the arm from the first exposure position into the second exposure position, the extension of the imaginary center axis of the rotational axis is arranged in the device disclosed in European Application 0 370 089 so that it lies immediately above the subject table. The distance between the subject table and the center axis is fixed, which means that most patients must undertake a certain lateral position correction when changing from a vertical exposure position into a lateral exposure position. Only a few patients have a breast size for which this device is suitable without such a correction, so that the imaginary center axis lies in axial alignment with the imaginary center axis of the compressed breast.